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Abstract

PurposeThe aim of the current study was to survey if vowel articulation in speakers with
Parkinson's disease (PD) shows specific changes in the course of the disease.Method67 patients with PD (42 male) and 40 healthy speakers (20 male) were tested and retested
after an average time interval of 34 months. Participants had to read a given text
as source for subsequent calculation of the triangular vowel space area (tVSA) and
vowel articulation index (VAI). Measurement of tVSA and VAI were based upon analysis
of the first and second formant of the vowels /α/, /i/and /u/ extracted from defined
words within the text.ResultsAt first visit, VAI values were reduced in male and female PD patients as compared
to the control group, and showed a further decrease at the second visit. Only in female
Parkinsonian speakers, VAI was correlated to overall speech impairment based upon
perceptual impression. VAI and tVSA were correlated to gait impairment, but no correlations
were seen between VAI and global motor impairment or overall disease duration. tVSA
showed a similar reduction in the PD as compared to the control group and was also
found to further decline between first and second examination in female, but not in
male speakers with PD.ConclusionsMeasurement of VAI seems to be superior to tVSA in the description of impaired vowel
articulation and its further decline in the course of the disease in PD. Since impairment
of vowel articulation was found to be independent from global motor function but correlated
to gait dysfunction, measurement of vowel articulation might have a potential to serve
as a marker of axial disease progression.

Many authorities have drawn attention to the difficulties in clinically distinguishing Parkinson's disease (PD) from other parkinsonian syndromes. We assessed the clinical features of 100 patients diagnosed prospectively by a group of consultant neurologists as having idiopathic PD according to their pathologic findings. Seventy-six percent of these cases were confirmed to have PD. By using selected criteria (asymmetrical onset, no atypical features, and no possible etiology for another parkinsonian syndrome) the proportion of true PD cases identified was increased to 93%, but 32% of pathologically confirmed cases were rejected on this basis. These observations suggest that studies based on consultant diagnosis of PD, using standard diagnostic criteria, will include cases other than PD, thus distorting results from clinical trials and epidemiologic studies. The strict use of additional criteria can reduce misdiagnosis but at the cost of excluding genuine PD cases.

Voice quality variations include a set of voicing sound source modifications ranging from laryngealized to normal to breathy phonation. Analysis of reiterant imitations of two sentences by ten female and six male talkers has shown that the potential acoustic cues to this type of voice quality variation include: (1) increases to the relative amplitude of the fundamental frequency component as open quotient increases; (2) increases to the amount of aspiration noise that replaces higher frequency harmonics as the arytenoids become more separated; (3) increases to lower formant bandwidths; and (4) introduction of extra pole zeros in the vocal-tract transfer function associated with tracheal coupling. Perceptual validation of the relative importance of these cues for signaling a breathy voice quality has been accomplished using a new voicing source model for synthesis of more natural male and female voices. The new formant synthesizer, KLSYN88, is fully documented here. Results of the perception study indicate that, contrary to previous research which emphasizes the importance of increased amplitude of the fundamental component, aspiration noise is perceptually most important. Without its presence, increases to the fundamental component may induce the sensation of nasality in a high-pitched voice. Further results of the acoustic analysis include the observations that: (1) over the course of a sentence, the acoustic manifestations of breathiness vary considerably--tending to increase for unstressed syllables, in utterance-final syllables, and at the margins of voiceless consonants; (2) on average, females are more breathy than males, but there are very large differences between subjects within each gender; (3) many utterances appear to end in a "breathy-laryngealized" type of vibration; and (4) diplophonic irregularities in the timing of glottal periods occur frequently, especially at the end of an utterance. Diplophonia and other deviations from perfect periodicity may be important aspects of naturalness in synthesis.

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